In the conventional methods to prepare microcapsules such as solvent evaporation method from W/O type, O/W type or W/O/W type emulsions for the purpose of stabilizing unstable compounds or releasing the incorporated compounds at a constant rate, only almost spheric and symmetric microcapsules can be produced.
The present inventor previously innovated the asymmetric (hemisperical) micro- or mili-capsules having three-layers structure as pharmaceutical preparation (Kanji Takada, International Application No. PCT/JP99/06602, An oral formulation for gastrointestinal drug delivery). By means of the conventional preparation methods of microcapsules, those micro- or mili-capslues cannot be produced in large scale. In addition, it is impossible to attain the complete loading efficieny (almost 100%) of the objective substance inside the micro-capsules. The conventional preparing methods of micro-capsules have a low loading efficiency of the objective substance inside the micro-capsules, and have a low recovery due to the wide variation of the particles size of the obtained micro-capsules.
Many preparation methods of micro-capsules including solvent evaporation method from W/O/W emulsions have been developed up to now. However, the micro-capsules obtained by these techniques have spherical shapes. Also, in the conventional methods, it was extremely difficult to load the objective substance into the micro-capsules with loadimg efficiency of 100%.